Solution-processed organic photovoltaics have been recognized as one of the most promising alternative next-generation green technologies to inorganic solar cells. They have drawn much attention due, in part, to their potential eco-friendliness and low-cost conversion of solar energy to clean electricity due to, e.g., their solution processability, light weight and flexibility of organic solar cells (OSCs).
As a result of the remarkable improvements in power conversion efficiencies (PCEs) of up to 13.2% that have been achieved for single-junction bulk heterojunction (BHJ) polymer OSCs, small molecule (SM) BHJ OSCs are under intense study recently.
Small molecule BHJ OSCs have several advantages over single-junction BHJ polymer OSCs. Such advantages include, e.g., defined molecular structure and molecular weight, high purity, and good batch-to-batch reproducibility of small molecules in comparison with their polymer counterparts.
These properties have the potential to allow researchers to better understand the relationships between the molecular structures and device performance. They may also provide a path to design higher performance photovoltaic materials and finally realize commercial applications especially when the PCEs of solution-processed small molecule based solar cells have increased dramatically up to 10% for single layer cells structure, which is closing the gap to the much widely investigated polymer based solar cells.
Inspired by the natural photosynthetic systems which utilize chlorophylls to absorb light and carry out photochemical charge separation to store light energy, porphyrins and their derivatives have been explored as the active materials from the beginning of OSC studies. However, the PCEs of the BHJ OSCs based on them have traditionally been very low.
It is an objective of the present disclosure to provide materials for building BHJ OSC to achieve higher PCEs.